Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1992-10-06
1994-07-05
Niebling, John
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204419, G01N 2726
Patent
active
053264525
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a glass electrode having a membrane of ion sensitive glass characterized with a dispersed filling material therein.
Glass electrodes have been known since the beginning of this century and are i.e. briefly described in ROPPS Chemie-Lexicon, 8th edition (1985) page 1491. A glass electrode comprises i.e. a very thin membrane of ion sensitive glass. The thin membrane is extremely fragile and gradually many attempts have been made in order to develop more rugged glass electrodes. These more rugged glass electrodes are primarily of the solid state type meaning that the ion sensitive glass is supported by a solid material, for example a metal, an electrically conductive glass and/or a ceramic material. Traditional glass electrodes, on the contrary, have an Unsupported glass membrane which separates an inner liquid and the environments.
Applicant has described glass electrodes of the solid state type in the specifications of British Patent No. GB 2073891, U.S. Pat. No. 4,632,732 and Danish Patent No. DK 151918, respectively. Other descriptions of glass electrodes of the solid state type are found in U.S. Pat. No. 4,133,735 (Afromowitz); in U.S. Pat. No. 4,458,685 (Sumitomo), respectively and in a number of earlier patent specifications, for example U.S. Pat. No. 3,853,731 (Owens-Illinois). The contents of the patent specifications stated above are considered incorporated into the present application by reference.
Further improvement on the strength of the glass membrane is, however, still required and the purpose of the invention is, therefore, to provide such a further improved glass electrode. This is achieved by the glass electrode of the present invention.
The glass electrode according to the invention may depending on the ion sensitive glass employed to the membrane be applied for determination of any ion which can be determined by a glass electrode. These ions are especially H.sup.+ or other cations such as alkaline metal cations, alkaline earth metal cations and certain organic cations, for example Li.sup.+, Na.sup.+, K.sup.+, Rb.sup.+, Cs.sup.+, NH.sub.4 +and Ag.sup.+. In a preferred embodiment of the . invention the ion sensitive glass is a pH sensitive glass.
The glass electrode according to the invention comprises a filling material with higher tensile strength than the matrix of ion sensitive glass, preferably a filling material with considerably higher tensile strength than the matrix. In this respect considerably higher tensile strength means twice the tensile strength or more, particularly about five times as high tensile strength (measured as bending tensile strength). Typically, a suitable filling material has tensile strength of 200-1000 MPa, especially approx. 500 MPa whereas the matrix has tensile strength of approx. 100 MPa. The filling material lies as a separate phase in the matrix.
Due to high temperature processes in the manufacturing of glass electrodes it is preferred that the filling material has a thermal expansion coefficient which is compatible with the thermal expansion coefficient for the ion sensitive glass. Hereby the tensions are reduced and consequently development of cracks in the product. In practice this is considered the case when the thermal expansion coefficient of the filling material ranges within the thermal expansion coefficient .+-.20% of the ion sensitive glass.
In order to ensure a massive, pinhole-free structure of the membrane of filling material-containing ion sensitive glass the filling material should be able to enter into intimate connection with the glass phase. Other criterions for the selection of filling material are that the filling material must not affect the ion sensitivity of the glass and must be chemically inert to the frequently occurring test solutions the ion content of which is to be determined, and further that the filling material must not show redox sensitivity. If the criterions mentioned above are fulfilled it will be possible to maintain the same measuring qualities for the electrodes according to the invention
REFERENCES:
patent: 3713992 (1973-01-01), Akazawa
patent: 3853731 (1974-12-01), Gray et al.
patent: 4052285 (1977-10-01), Dobson
patent: 4133735 (1979-01-01), Afromowitz et al.
patent: 4458685 (1984-07-01), Hiramoto et al.
patent: 4632732 (1986-12-01), Fog et al.
patent: 4836907 (1989-06-01), Pederson
Rompps Chemie-Lexikon, 8th Edition (1985) p. 1491.
Linnet Niels D.
Roed Gjerloff
Bell Bruce F.
Cave Bryan
Klein David M.
Niebling John
Radiometer A/S
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